Q1: State the modern Cell Theory.
Answer: Modern cell theory explains that cells are the basic units of life and new cells come only from old cells.
✅ Modern Cell Theory (Key Points):
- All living organisms are made of cells and cell products.
- The cell is the basic structural and functional unit of life.
- New cells arise from pre-existing cells (Omnis cellula e cellula — Virchow).
- Cells contain hereditary material (DNA/RNA) which passes to daughter cells.
- All metabolic reactions and energy flow occur inside cells.
🔑 Memory Line:
Cell makes life; cell continues life.
Q2: Why is the plasma membrane described as having a "Fluid Mosaic" structure?
Answer: The plasma membrane is called fluid mosaic because it is a fluid lipid bilayer and proteins are embedded in it like a mosaic pattern. The proteins and lipids can move sideways, which makes the membrane flexible.
✅ Key Points:
- Proposed by Singer and Nicolson (1972).
- Mosaic: Proteins are scattered/embedded like tiles.
- Fluid: Lipids (and some proteins) show lateral movement.
- Fluidity helps in:
- Cell growth
- Secretion
- Endocytosis/exocytosis
- Cell division
🔑 Memory Trick:
Fluid = moving lipids, Mosaic = embedded proteins.
Q3: Differentiate between Prokaryotic and Eukaryotic cells.
Answer: Prokaryotic cells are simpler and do not have a true nucleus, while eukaryotic cells are more complex and have a true nucleus and organelles.
| Feature | Prokaryotic Cell 🦠 | Eukaryotic Cell 🧬 |
|---|---|---|
| Nucleus | Absent (DNA in nucleoid) | Present (true nucleus with membrane) |
| Organelles | Absent | Present (ER, Golgi, mitochondria etc.) |
| Ribosomes | 70S | 80S (cytoplasm) |
| Size | Smaller (approx. 0.1–5 µm) | Larger (approx. 10–100 µm) |
| Examples | Bacteria, cyanobacteria | Plants, animals, fungi, protists |
🔑 Key Memory Line:
Prokaryote = no nucleus; Eukaryote = true nucleus.
Q4: Explain the term "Endomembrane System". Which organelles are included in it?
Answer: The endomembrane system is a group of organelles that work together to make, modify, pack, transport, store, and digest materials inside the cell.
✅ Included Organelles:
- Endoplasmic Reticulum (ER)
- Golgi apparatus
- Lysosomes
- Vacuoles
❌ Not Included: Mitochondria, chloroplasts, peroxisomes
🔑 Key Point:
Endomembrane system = coordinated transport + packaging + digestion.
Q5: Why are mitochondria and chloroplasts called "semi-autonomous organelles"?
Answer: They are called semi-autonomous because they have some of their own genetic and protein-making machinery, so they can make some proteins on their own, but they still depend on the nucleus for many proteins.
✅ Key Points:
- Have circular DNA
- Have 70S ribosomes
- Can synthesize some proteins
- Multiply by fission
🔑 Memory Line:
Own DNA + own ribosomes = semi-autonomous.
Q6: Describe the structure and function of the nucleolus.
Answer: The nucleolus is a dense, round body inside the nucleus. It has no membrane and it is the place where rRNA is made and ribosomal subunits start forming.
✅ Key Points:
- Non-membrane-bound structure
- Present in nucleoplasm
- Site of rRNA synthesis
- Helps in ribosome formation
🔑 Exam Line:
Nucleolus = rRNA factory.
Q7: Classify chromosomes based on the position of the centromere.
Answer: Chromosomes are classified based on where the centromere lies on them.
✅ Types (with easy shapes):
- Metacentric: Centromere in middle → V-shape (equal arms)
- Sub-metacentric: Centromere slightly off centre → L-shape (unequal arms)
- Acrocentric: Centromere near one end → J-shape (one very short arm)
- Telocentric: Centromere at the end → I-shape
🔑 Memory Trick:
Meta-middle, Sub-slight, Acro-almost end, Telo-terminal.
Q8: What are mesosomes? What are their functions in bacteria?
Answer: Mesosomes are infoldings of the bacterial plasma membrane. They help increase surface area and support important activities like respiration and DNA distribution.
✅ Functions (High-Yield):
- Cell wall formation
- DNA replication and distribution to daughter cells
- Respiration (since mitochondria are absent)
- Secretion and increased membrane surface area
🔑 Mnemonic:
Mesosome = W-D-R-S (Wall, DNA, Respiration, Secretion)
Q9: Describe the structure of a centriole.
Answer: A centriole is a cylindrical structure made of microtubules arranged in a 9+0 pattern. It has nine triplets on the outside and no central microtubules.
✅ Key Points:
- 9 peripheral triplets of microtubules
- Made of tubulin
- Central protein part = hub
- Hub connected by radial spokes
🔑 Memory Line:
Centriole = 9 triplets, no central pair (9+0).
Q10: Differentiate between RER and SER.
Answer: RER looks rough because ribosomes are attached to it, so it makes proteins. SER is smooth because it has no ribosomes, so it makes lipids and steroids.
✅ Key Points:
- RER: ribosomes present → protein synthesis
- SER: ribosomes absent → lipid synthesis and steroid hormone synthesis
🔑 One-Liner:
RER = proteins, SER = lipids.
Q11: What are lysosomes and how are they formed?
Answer: Lysosomes are small membrane-bound sacs containing digestive enzymes. They are formed when the Golgi apparatus packages these enzymes into vesicles.
✅ Key Points:
- Formed by Golgi apparatus
- Contain hydrolytic enzymes (lipase, protease, carbohydrase)
- Work best at acidic pH
- Digest worn-out organelles and foreign particles
🔑 Exam Line:
Lysosomes = digestive bags made by Golgi.
Q12: What is the significance of the 9 + 2 arrangement in cilia and flagella?
Answer: The 9+2 arrangement is the special microtubule pattern in the axoneme that makes bending and movement possible in cilia and flagella.
✅ Key Points:
- Axoneme has:
- 9 peripheral doublets
- 2 central singlets
- Helps in motility and bending movement
🔑 Memory Line:
9+2 = movement arrangement.
Q13: What constitutes the cell envelope in prokaryotes?
Answer: The cell envelope is the outer protective covering of bacteria, made of three layers.
✅ Three Layers:
- Glycocalyx (slime layer/capsule)
- Cell wall
- Plasma membrane
🔑 Memory Trick:
Envelope = G-C-P (Glycocalyx–Cell wall–Plasma membrane).
Q14: Differentiate between primary and secondary cell walls.
Answer: The primary wall is thin and flexible in young cells, while the secondary wall is thick and rigid in mature cells.
✅ Key Points:
- Primary wall:
- Young growing cells
- Thin, elastic
- Allows growth
- Secondary wall:
- Formed after growth stops
- Thick, rigid
- Provides strength
🔑 One-Line:
Primary = growing wall, Secondary = strengthening wall.
Q15: What is a satellite chromosome?
Answer: A satellite chromosome is a chromosome that shows a secondary constriction, making a small separated part that looks like a satellite.
✅ Key Points:
- Secondary constriction present
- Small detached part = satellite
🔑 Memory Line:
Secondary constriction gives satellite appearance.